1. Field of the Invention
This invention relates to refractory-binder coated compositions. More particularly, it relates to an inorganic binder composition which may usefully be employed, in combination with refractory materials, in preparing refractory-binder coated compositions. This invention is especially related to refractory-binder compositions which may be applied to woven, knitted or non-woven fabrics constructed from textile yarns to provide them with high temperature resistance and flame resistance.
2. Description of the Prior Art
Ceramics and/or glass fibers have been used herebefore to prepare high temperature electrical insulating tape. U.S. Pat. No. 4,358,500 discloses refractory coated insulating compositions wherein the refractory coating, comprising refractory materials and an inorganic bonding agent, is formed on the surface and, necessarily, the interstices of a porous base fabric, such as a knitted fiberglass fabric. In the presence of extreme temperatures and heat, the refractory materials fuse into the softened surface of the base fabric, enabling it to withstand intense heat, flame impingement, flame abrasion, and elevated temperatures well beyond the normal temperature limitations of the fabric. The resulting fabric structure will have ceramic qualities and will not soften, melt, drip or lose its insulating properties.
Commonly assigned patent application Ser. No. 338,850 and U.S. Pat. Nos. 4,375,493 and 4,396,661 relate to multi-functional fabric compositions having a refractory coating on one side of the base fabric and a different coating providing a different function on the other side, i.e., the '850 application--a vapor barrier coating, the '493 patent--a conductive coating and the '661 patent--a dielectric coating.
The inorganic bonding agent disclosed in U.S. Pat. No. 4,358,500 is prepared from colloidal silica, monoaluminum phosphate (MAP) and aluminum chlorohydrate (ACH) by adding the MAP and ACH separately to the colloidal silica which acts as a liquid moderator. Although the compositions containing the inorganic bonding agent of U.S. Pat. No. 4,358,500 may be exposed to high temperatures, no products of combustion in the form of smoke or fumes are produced as with other prior art coated fabrics. Further, the refractory coated compositions prepared with the inorganic bonding agent proved superior to inorganic coatings available for use on fabrics or paper substrates. The latter inorganic coatings could be damaged by water. They could be wet by water and the water could solvate the coating to the point of causing the inorganic coating to dissociate itself from the substrate. Although other binders, such as the acrylics, inhibited this wetting action, they would burn off when subjected to flame and high temperature. The refractory coated substrates disclosed in the '500 patent, on the other hand, are not wetted by water and are not subject to the solvation action of water as are other inorganic coatings. However, despite these advantages, the refractory coated compositions of the '500 patent exhibit a very undesirable feature. This refractory coating must be applied to a porous fabric so that the coating will be placed in the interstices of the fabric. This is necessary to achieve the formation of the refractory coating on this fabric. However, this requires the use of a larger quantity of the refractory coating when preparing these compositions to the extent that the coating in many instances constitutes about 50% of the overall weight of the impregnated base fabric. The result of all this is that when this coated fabric is flexed, the bond of the refractory coating to the substrate is disrupted and some particles may be released to the surface resulting in "dusting" of the coating. This, of course, is highly undesirable despite the very desirable features of flame and high temperature resistance which are exhibited by these refractory coated compositions.
It is an object of this invention to provide an improved inorganic bonding agent (binder) which may be usefully employed in preparing refractory-binder coated compositions and which will provide an intimate bond between the refractory coating and the fibrous surface of the yarn comprising the fabric so that the coating will not dissociate itself from the fiber upon flexure of the coated composition.
It is another object of this invention to provide refractory coated fabric compositions which will not exhibit "dusting" of the refractory coating in use.